Fast response r-f switching matrix



May 2, 1967 -K. D.'MGDONALD ETAL 3,317,748

FAST RESPONSE R-F SWITCHING MATRIX Filed April 21, 1964 4 Sheets-Sheet 1 May 2 1967 K. D. MCDONALD ETAL 3,317,748

FAST RESPONSE R-F SWITCHING MATRIX Filed April 2l, 1964 4 Sheets-Sheet 2 hay. M50.

INVENTORS Aff/7W MdA//M Va/V46 J. aLoa-/v May-2 1967 K. D. MCDONALD ETAL 3,317,748

FAST RESPONSE R-F SWITC'HING MATRIX Filed April 2l, 1964 4 Sheets-Sheet 5 Fl' G, 3a?

(m0 J7 A .,fp vvv '-f-c May 2, 1957 K. D. MCDONALD ETAL 3,317,748

FAST RESPONSE R-F SWITCHING MATRIX Filed Aprilzl, 1964 4 Sheets-Sheet 4 ma .Pw www .wwv mf. A@ uw mm Sh AMY W United States Patent Otlice 3,3l7,748 Patented May 2, 1967 3,317,748 FAST RESPONSE R-F SWITCHING MATRIX Keith D. McDonald, Alexandria, Va., and Thomas S.

Golden, Washington, D.C., assignors to the United States of America as represented by the Secretary of the Air Force Filed Apr. 21, 1964, Ser. No. 361,601 2 Claims. (Cl. 307--88.5)

This invention relates to apparatus for switching electrical signals, and more particularly, to a fast response radio frequency swithcing matrix by means of which one or several R-F signal inputs may be selectively switched in a rapid manner to one or a number of R-F output channels by a single or multiple channel input signal.

Prior art for performing the function of a fast response switching matrix consists `of principally electrically or mechanically actuated mechanical R-F switching devices such as coaxial or waveguide type switches arranged in a manner to perform the required operation. The prin cipal disadvantages of the mechanical type R.F. switching devices are: (a) slow response time to activate or deactivate the R-F switched path, (b) larger actuation power required due to the necessity for overcoming appreciable mechanical inertia in a short period of time, (c) complexity and close mechanical tolerances involved in the mechanical switching devices, and (d) large spatial requirements due to physical considerations involved in maintaining the proper characteristic impedance, suficient structural rigidity to operate at the required speeds, and providing adequate driving means for rapid switching operation.

This invention contemplates the use of a matrix of electrically actuated semiconductor control elements multiply connected to a set or -R-F inputs in such a manner that path selection of any input signal to any output channel may be easily achived. This arrangement of the electronic switching elements, in this case highcurrent semiconductor diodes, achieves a high degree of isolation between the input signal and the output channel in the off mode of matrix element operation.

Other `advantages of a fast response R-F switching matrix vover conventional methods of R-F switching are: (a) faster response time of the R-F switching circuit to electrical actuation signals; (b) completely electronic operation of the device enabling greatly decreased fabrication and mechanical tolerance difficulties, reduced spatial needs and lower actuating energy requirements; and (c) increased flexibility of the many matrix arrangements available due to employment of basic buildingblock circuit elements which may be fabricated in modular form, such as by printed wiring cards.

It is, accordingly, a general object of the present invention to provide a new and improved fast response R-F switch.

It is another object of the present invention to provide an improved signal routing circuit.

A further object of the present invention is to provide a switching network whereby one or more signal inputs may be selectively switched in a rapid manner to one or more output channels by a single or multiple channel input signal.

A further understanding of this invention may be gained from a consideration of the following detailed description taken in conjunction with the following drawings in which:

FIGURE la shows the available input and output lines of the switching matrix;

FIGURE 1b shows in general form the switching action occurring when a given input line is activated;

FIGURE 2a shows a typical matrix element;

FIGURE 2b shows a D.C. or pulse path through the matrix element in the on condition;

FIGURE 2c shows a low impedance path for an R-F input in the on condition;

FIGURE 2d shows the D.C. or pulse path in the olf condition;

FIGURE 2e shows the R-F path for the oit condition;

FIGURE 3a is a simpliiied circuit schematic for the matrix switching element;

FIGURE 3b shows the equivalent circuit of FIGURE 3a when the selector switch is Iopen;

FIGURE 3c shows the equivalent circuit of FIGURE 3a when the selector switch is closed; and

FIGURE 4 shows the experimental switching matrix circuit coniguration embodying the invention.

Considering FIG. 4 in more detail, there is depicted a schematic of the experimental switching matrix configuration utilized as the principal control element for rapid switching of R-F phase related signals to a series of R-F output channels. The construction used to fabricate this circuit for system use involved separating the circuit into a number of similar modules which could be attached to a wiring interconnection framework. The region enclosed by the dotted line 29 is a typical circuit module which took the form of a printed wiring card or matrix card. Since these module circuits are all identical, it is only necessary to show the means of interconnecting the cards with the input and output R-F channels, the input actuation pulses, and each other.

FIG. 2 shows in simplified form a typical matrix element in its various stages of operation. FIG. 2a shows the make up of the matrix element. IReferring to FIG. 2a, the matrix element comprises resistors 11 and 12 connected together at ground terminal 27; a switching pulse Ed may be applied at terminal 26, which is also the junction of resistor 11 and diode 13; a switching pulse may also be applied at terminal 29, which is also the junction of resistor 12 and diode 14; the cathodes of diodes 13 and 14 are tied together at terminal 28, which is also the terminal for the parallel combination of capacitor 16 and resistor 15, the other side of which is connected to terminal 27. An R-F choke is connected from terminal 28 to terminal 30, which is also the junction of diodes 18, 19, and 20, with the cathode of diode 19 connected to the anodes of diodes 13 and 20. The cathode of diode 18 is connected to terminal 31, the R-F output terminal; the cathode of diode 20 is connected to terminal 32, the R-F input terminal; resistor 22 is connected from terminal 32 t-o terminal 33, to which a D.C. bias of value Ec is applied. Resistor 24 is connected between terminals 31 and 33. Resistor 23 is connected to terminal 33 and terminal 34, the junction terminal to which the anode of diode 19 is also connected; capacitor 35 is also connected between terminal 34 and ground. The R-F input is applied through capacitor 21 to terminal 32, and the R-F output is fed out from terminal 31 through capacitor 25.

FIG. 2b shows the D.C. or pulse path through the matrix element for a value of Ed=2Ec- A positive pulse Ed of value equal to approximately ZEC will cause the a anodes of diodes 13, 18, and 20 to be positive with respect to their cathodes, and therefore will cause these diodes to conduct and present a low impedance path in the on condition. R-F choke 17 oifers no resistance to the D.C., but presents a high impedance to the R-F energy. The path for an R-F input at terminal 32 is as shown in FIG. 2c, which shows that the conducting diodes 18 and 20 present a low impedance path for the R-F from terminal 32 to 30 to the output at terminal 31'. The R-F choke between terminals 28 and 30 serves to isolate the pulse circuit from the R-F circuit.

The absence of a signal Ed at terminal 26 will cause diodes 13, 18, and 20 to change to a non-conducting state; diode 19 will be in a conducting state, so that the D.C. or pulse path for this olf condition will be as shown in FIG. 2d; the R-F path for this condition is shown at FIG. 2e, which shows that an R-F signal applied at terminal 32 will face two parallel branches to ground of high impedance paths, thus efectively isolating the R-F input terminal 32 from R-F output terminal 31; the R-F choke 17 again serves to isolate the pulse circuit from the R-F circuit.

FIG. 3 illustrates the basic electrical element of a fast response R-F switching matrix. F-IG. 3a is a simplified circuit schematic for the matrix switching element. In FIG. 3a, selector switch S1 corresponds to an actuating signal pulse when in the closed position, and to an absence of a pulse in the open position. As in most switches, the switching element is arranged to exist in one or two possible states, on or offf For selector switch S1 shown in FIG. 3 as open, the negative supply voltage --Ec is applied to terminal through resistor 16 to terminal 11 and is then impressed on point P through R-F choke 17, which isolates the power supplies from the R-F circuit, but provides a low impedance path for the D.C. (pulse) switching voltages. The anodes of diodes 1S and 20 are tied together at point P, and also the cathode of diode 19; the anode of diode 19 is connected to ground. The cathode of diode 20 is connected to terminal 12, and the cathode of diode 18 is connected to terminal 13. The R-F input is connected through terminal I1 to capacitor 21, and the R-F output is fed from terminal 13 through capacitor 25 through terminal I2. Resistor 22 is connected from terminal 12 to terminal 14, to which a D.C. voltage -i-Ec is applied, and resistor 23 is connected from terminal 14 to terminal 13.

With selector switch S1 open, point P is at Ec volts, and diodes 18 and 20, which branch off from point P to provide a path for the R-F energy (when conducting), are reverse biased and therefore non-conducting, presenting a low admittance path (principally determined by the diode isusceptance) to the R-F energy. Diode 19 is returned to ground and is therefore conducting, appearing as a high admittance across P. The R-F input at J1 is therefore shunted by the high admittance of diode 19 to ground. The potentiometer action here provides a large off condition isolation between the input and output lines.

Isolation is further improved by the divider action of diode 18, which is now a low admittance, and resistor 22. lOutput to input isolations of the order of 60 to 70 db for this type of conguration operating in the 2-30 mc. region have been realized.

When S1 is closed, the matrix element rapidly switches to the on state. The switching time is limited by the response time of the diode and the rise time of the associated RLC driving circuit. This response time can be reduced to the order of microseconds or less, which is at least three orders of magnitude faster than the best mechanical R-F switches presently in use. Closing S1 causes point P to change from -Ec to -l-Ec, thereby reversing the conduction characteristics of all of the diodes in the `R-F switching element. Diodes 18 and 20 are switched to conduction and appear as high admittance paths between input and output. lDiode 19 is switched to its non-c-onducting state and therefore presents a low admittance, again principally susceptance, to the junction at point P. The R-F path through the matrix element is principally a high conductance path with only minor losses. The simplied equivalent circuits of FIG. 3a for the switch S1 open and closed are shown in FIGS. 3b and 3c, respectively.

FIG. 4 shows one application of a typical matrix element described in FIG. 2. R-F inputs on lines 18, 19, and 20 are switched as described previously by a positive pulse Ed, on line 25 to lines 11, 12, 14, 15 and 16. While FIG. l is used to show three input R-F lines switched to ve output R-F lines, it can be readily seen that one or several R-F signal inputs may be switched to one or any number of R-F output lines by a single or multiple channel input signal.

In addition to the fundamental simplicity of the basic elements of the fast response R-F switching matrix, there are many other advantages in using this circuit. The reliability of the switching matrix should be excellent, since there are no moving parts to cause performance degradation with use. All elements of the matrix may be designed to operate well within rated capacities. The device lends itself easily to miniaturizati-on and modular construction. In performance, the switching matrix provides a high-conductance, low-loss path for R-F in the on condition, and presents a low conductance path with a high degree of input-output isolation in the olf condition. The device may maintain a reasonably good match between source and load in the on condition, having a small value of shunt admittance in this state. The device is inherently broad-band and should perform very well over a considerable range of frequencies. Es-

sentially the fast response R-F switching matrix replaces a somewhat complicated and reasonable close-tolerance mechanical switching system with a completely electronic circuit arrangement capable of operation at a greatly increased switching rate.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A diode switching circuit comprising:

a. a source of bias voltage;

b. an R-F choke;

c. a signal input terminal;

d. a signal output terminal;

e. a pair of resistors connected in series between the signal input terminal and the signal output terminal, the junction of the two resistors connected to the bias source;

h. a biasing resistor interposed between the single diode signal input and the signal output terminals, the junction of the two diodes connected to the R-F choke and the diodes being so poled that they are biased in the reversed direction;

g. a single diode connected to the junction of said pair of diodes in series and to the bias source, said single diode being biased in the forward direction;

l1. a biasing resistor interposed between the single diode and the bias source;

i. a grounded capacitor connected to the junction of said diode and biasing resistor;

j. switching means connected to the remote terminal of said R-F choke for the application of a voltage to overcome the reverse bias and apply a forward bias to said diodes, the switching means comprising a source of switching Voltage, a switching diode connected to the remote side of said R-F choke, a grounded resistor connected to the switching diode, wherein the switching voltage is connected to the junction of said resistor and said switching diode, said switching diode being poled so that the switching voltage applies a forward bias thereto;

k. and means for isolating said switching means from said switching voltage.

2. Apparatus as speci-fied in claim 1 wherein said isolating means comprise a grounded capacitor and resistor connected in parallel to the remote side of said R-F choke.

3,011,129 11/1961 Magleby 307-885 X OTHER REFERENCES Bell System Technical Journal, November 1961, page` 

1. A DIODE SWITCHING CIRCUIT COMPRISING: (A) A SOURCE OF BIAS VOLTAGE; (B) AN R-F CHOKE; (C) A SIGNAL INPUT TERMINAL; (D) A SIGNAL OUTPUT TERMINAL; (E) A PAIR OF RESISTORS CONNECTED IN SERIES BETWEEN THE SIGNAL INPUT TERMINAL AND THE SIGNAL OUTPUT TERMINAL, THE JUNCTION OF THE TWO RESISTORS CONNECTED TO THE BIAS SOURCE; (F) A BIASING RESISTOR INTERPOSED BETWEEN THE SINGLE DIODE SIGNAL INPUT AND THE SIGNAL OUTPUT TERMINALS, THE JUNCTION OF THE TWO DIODES CONNECTED TO THE R-F CHOKE AND THE DIODES BEING SO POLED THAT THEY ARE BIASED IN THE REVERSED DIRECTION; (G) A SINGLE DIODE CONNECTED TO THE JUNCTION OF SAID PAIR OF DIODES IN SERIES AND TO THE BIAS SOURCE, SAID SINGLE DIODE BEING BIASED IN THE FORWARD DIRECTION: (H) A BIASING RESISTOR INTERPOSED BETWEEN THE SINGLE DIODE AND THE BIAS SOURCE; (I) A GROUNDED CAPACITOR CONNECTED TO THE JUNCTION OF SAID DIODE AND BIASING RESISTOR; (J) SWITCHING MEANS CONNECTED TO THE REMOTE TERMINAL OF SAID R-F CHOKE FOR THE APPLICATION OF A VOLTAGE TO OVERCOME THE REVERSE BIAS AND APPLY A FORWARD BIAS TO SAID DIODES, THE SWITCHING MEANS COMPRISING A SOURCE OF SWITCHING VOLTAGE, A SWITCHING DIODE CONNECTED TO THE REMOTE SIDE OF SAID R-F CHOKE, A GROUNDED RESISTOR CONNECTED TO THE SWITCHING DIODE, WHEREIN THE SWITCHING VOLTAGE IS CONNECTED TO THE JUNCTION OF SAID RESISTOR AND SAID SWITCHING DIODE, SAID SWITCHING DIODE BEING POLED SO THAT THE SWITCHING VOLTAGE APPLIES A FORWARD BIAS THERETO; (K) AND MEANS FOR ISOLATING SAID SWITCHING MEANS FROM SAID SWITCHING VOLTAGE. 